1. Field of the Invention
The present invention relates to an output device, image data conversion device, and method which outputs pixel data corresponding to a color material used by a printing means to the printing means.
2. Description of the Related Art
As functions of an image processing device used when a printing apparatus prints, those shown in FIG. 1 are conventionally known.
Referring to FIG. 1, reference numeral 101 denotes an image construction unit. The image construction unit 101 rasterizes received print data to generate drawing data formed of a series of pixel data. Reference numeral 102 denotes an image buffer. The image buffer 102 temporarily stores drawing data generated in the image construction unit 101.
Reference numeral 103 denotes a color correction unit. The color correction unit 103 reads out each pixel data of drawing data stored in the image buffer 102 and performs color correction. This color correction matches the color gamut of an input color space with that of an output color space. Reference numeral 104 denotes a color separation unit. The color separation unit 104 converts color-corrected drawing data into density data (color material density data) for each color material. Japanese Patent Laid-Open No. 2004-274131 proposes an exemplary conversion method using a look-up table (cache memory).
Reference numeral 105 denotes a quantization unit. The quantization unit 105 converts color material density data into color material amount data (operation data for operating a print head of the printing unit 107) corresponding to the resolution and number of gray levels of the printing unit 107. Reference numeral 106 denotes a print buffer. The print buffer 106 stores color material amount data required for a predetermined operation cycle (a process for one scanning in an inkjet printing unit, and a process for one page in an electrophotographic printing unit). With this arrangement, the printing unit 107 can continuously perform the predetermined operation cycles.
The printing unit 107 prints on a medium such as a paper sheet based on color material amount data. As a printing method, for example, an inkjet method, electrophotographic method, or the like is available.
In this arrangement, the capacity of the print buffer 106 depends on the structure of the printing unit 107. FIG. 2 is a view schematically showing the structure of an inkjet printing unit. As shown in FIG. 2, print heads of respective colors are arranged in the main scanning direction, and each print head has a plurality of nozzles arranged in the sub-scanning direction. Accordingly, the amount of color material amount data for one scanning in the printing unit 107 is (the number of dots in the main scanning direction)×the number of nozzles×the number of colors (the number of planes). The number of dots in the main scanning direction is determined by a print width and output resolution in the main scanning direction.
On the other hand, in order to improve the output image quality of a printing apparatus, the output resolution is improving and the number of ink colors is increasing.
As the output resolution improves and the number of ink colors increases, the capacity required of the print buffer 106 is significantly increasing. Assume that four-color printing with an output resolution of 600 dpi in the main scanning direction is compared with eight-color printing with an output resolution of 4800 dpi in the main scanning direction. When the number of nozzles is the same, the amount of color material amount data for one scanning is sixteen times larger in the latter case. For this reason, an increase in the cost of the print buffer along with improvement of the output image quality is obviously becoming a problem.
Also, when a look-up table used for color space conversion in a printing apparatus as described above is utilized by storing it in, for example, a dynamic RAM, a read operation of grid point data takes time and color space conversion delays. As a result, the whole printing process also delays. For this reason, in the printing apparatus as described above, it is demanded to reduce the processing load of color space conversion to prevent its delay.